The purpose of this project is to investigate the mechanisms which control feeding behavior in normal and obese monkeys. Experimentally induced obese monkeys, spontaneously obese monkeys, and normal controls will be used in order to establish the nature of the metabolic and hormonal signals controlling ingestive behavior. Because complex interactions of both hormones and fuels probably underlie both the regulation of intake and body adiposity, it is important to examine a number of potential signals simultaneously and under varied conditions. Baseline data will clarify the relationships between meal size and pre-and post-meal intervals in monkeys. Simultaneously moment to moment determinations of changes in substrate and hormone levels will be carried out and correlated with shifts in feeding patterns. Hypotheses concerning the role of specific humoral factors controlling feeding will be tested by altering potential signals via intravenous and intraarterial infusions. In order to analyze the contribution of both known and unknown factors in feeding regulation, the effects of the entire configuration of blood-borne constituents will be examined by means of the cross-circulation of pairs of monkeys who differ in metabolic state (one monkey fed and its partner deprived) or in adiposity (one obese, one of normal weight). Simultaneously changes in feeding patterns, hunger, satiety, fuels, and hormones will be monitored. Results will contribute to the understanding of disturbances of feeding behavior, body weight, and control, and the regulation of metabolism, and will have implications for the possible prevention or therapeutic management of obesity.